In2Te3 thin films: a promising nonlinear optical material with tunable nonlinear absorption response

Abstract

A series of In₂Te₃ thin films with various thicknesses was prepared on fused quartz substrate using a radio-frequency magnetron sputtering method. After annealing, the surface morphology, structure and linear optical absorption of these films was investigated. By performing an open aperture Z-scan technique with femtosecond pulses under 800 nm and 400 nm wavelengths, both the sign and magnitude of nonlinear absorption coefficient can be deduced. The experimental results show that In₂Te₃ thin films exhibit a large and ultrafast third-order nonlinear optical absorption response. Interestingly enough, a turnover from saturation absorption to reverse saturation absorption is observed by adjusting the film's thickness. Herein, a three-level model is presented to determine the tuning behavior and the competition mechanism between ground state absorption and excited state absorption. Moreover, the ultrafast pump-probe experiment furnished evidence of a nonlinear absorption difference, which was mainly caused by the density of defect states.